Iran's nuclear program began under Shah Mohammad Reza Pahlavi in the 1950s as part of the U.S. Atoms for Peace initiative. In 1967, Iran established the Tehran Nuclear Research Center with a U.S.-supplied 5 MW research reactor. During the 1970s, Iran pursued ambitious plans for up to 20 nuclear power plants (starting the Bushehr reactors with German assistance), but progress halted after the 1979 Islamic Revolution and the Iran–Iraq War. Iraq's use of chemical weapons during that war influenced Iran's post-revolution leaders to secretly revive a weapons-related nuclear program in the mid-1980s. By the 1990s, Iran was rebuilding its nuclear infrastructure: it sought a nuclear fuel cycle (mining, conversion, enrichment) and covertly obtained centrifuge designs from the Pakistani Abdul Qadeer Khan network. Construction of the Bushehr 1000 MWe power reactor resumed with Russian help and was completed in 2011 under IAEA safeguards.
Iran's nuclear activities remained mostly clandestine until 2002, when dissidents revealed undeclared facilities at Natanz (uranium enrichment) and Arak (heavy water reactor). This sparked an international crisis. Under pressure, Iran agreed in late 2003 to suspend enrichment and signed the IAEA Additional Protocol, amid an EU-3 (UK, France, Germany) negotiation effort. However, these voluntary limits collapsed after the election of Mahmoud Ahmadinejad in 2005, and Iran resumed enrichment, leading the IAEA Board of Governors to find Iran in non-compliance and the United Nations Security Council to impose sanctions starting in 2006. Throughout the late 2000s, Tehran steadily expanded its enrichment capacity, including the secret construction of the Fordow underground enrichment plant, revealed in 2009, and accumulated low-enriched uranium, at one point reducing its estimated nuclear breakout time to a few months. Covert actions sought to slow Iran's progress (for example, the Stuxnet cyber-attack in 2010 targeted Iran's centrifuges), but the program continued to advance.
A diplomatic breakthrough came in 2015, when Iran and the P5+1 (US, UK, France, China, Russia, and Germany) reached the Joint Comprehensive Plan of Action (JCPOA). This agreement imposed strict limits on Iran's nuclear program, capping uranium enrichment at 3.67% U-235, shrinking Iran's enriched uranium stockpile to 300 kg, and requiring the Arak heavy-water reactor to be redesigned, in exchange for broad sanctions relief. The JCPOA was implemented in 2016 with the IAEA verifying Iran's compliance. However, in May 2018 the United States unilaterally withdrew from the accord, citing Iran's missile program, support of proxies, and aggressive regional policies; US sanctions were reimposed, and Iran responded from 2019 onward by violating JCPOA limits. By 2020–2021, Iran ended its enrichment restraint and began enriching to higher levels than allowed. As of 2025, Iran's nuclear program is far more advanced than a decade earlier, having expanded significantly in both scope and scale. In June 2025, the International Atomic Energy Agency (IAEA) found Iran non-compliant with its nuclear obligations for the first time in 20 years. Iran retaliated by launching a new enrichment site and installing advanced centrifuges.
History
1950s–1960s Iran's nuclear program was launched in the 1950s with the help of the United States. On 5 March 1957, a "proposed agreement for cooperation in research in the peaceful uses of atomic energy" was announced under the Eisenhower administration's Atoms for Peace program.
In 1967, the Tehran Nuclear Research Center (TNRC) was established, run by the Atomic Energy Organization of Iran (AEOI). The center consists of 11 departments that conduct research on most aspects of the nuclear fuel cycle, including departments for nuclear physics, isotope production, reactor research, analytical chemistry, nuclear electronics and fusion. The TNRC was equipped with a 5-megawatt nuclear research reactor supplied by US company American Machine and Foundry, which was fueled by highly enriched uranium.
In 1968, Iran signed the Nuclear Non-Proliferation Treaty (NPT). Iran ratified it in 1970, making Iran's nuclear program subject to IAEA verification.
A Central Treaty Organization nuclear sciences instituteMCKAY, H. The Cento Institute of Nuclear Science in Tehran. Nature 186, 513–515 (1960). https://doi.org/10.1038/186513a0 was moved from Baghdad to Tehran after Iraq left CENTO.
The participation of the United States and Western European governments in Iran's nuclear program continued until the 1979 Iranian Revolution that toppled the last Shah of Iran. Following the Revolution, most of the international nuclear cooperation with Iran was cut off. In 1981, Iranian officials concluded that Iran's nuclear development should continue. Negotiations took place with France in the late 1980s and with Argentina in the early 1990s, and agreements were reached. In the 1990s, Russia formed a joint research organization with Iran, providing Iran with Russian nuclear experts and technical information.
1970s The Shah summoned Akbar Etemad, a trained nuclear physicist, to the royal court in 1973, told him of his desire to launch a nuclear program, and asked Etemad to develop a master plan. Two weeks later, the shah met with Etemad again. He read the 13-page draft document Etemad had prepared, then turned to the prime minister and ordered him to undertake necessary actions to implement the plan. Thus, was launched Iran's nuclear program.
The Shah approved plans to construct up to 23 nuclear power stations by 2000.Iran's Nuclear Program: Recent Developments : "The Shah's plan to build 23 nuclear power reactors by the 1990s was regarded as grandiose, but not necessarily viewed as a "back door" to a nuclear weapons program, possibly because Iran did not then seek the technologies to enrich or reprocess its own fuel" In March 1974, the Shah envisioned a time when the world's oil supply would run out, and declared, "Petroleum is a noble material, much too valuable to burn ... We envision producing, as soon as possible, 23,000 megawatts of electricity using nuclear plants."
In an interview released June 23, 1974 by the French weekly Les Informations, Mohammad Reza Shah, replying to the question whether Iran would one day possess a nuclear weapon, is quoted as saying, “Certainly, and sooner than is believed, but, contrary to India, we have first thought of our people and then of technology. You see the result today.” In reply to questions on arms purchases, the Shah stated: “The Persian Gulf is a strategic zone of first importance. The smallest spark and everything blows up. The very sophisticated army that I maintain is my force de dissuasion et de frappe (deterrent and strike force). What do the French do with their bomb? I do the same with my resources.”Interview with the Shah, State Department Cable 1974 Paris 15305, June 24, 1974.
In the following day, 24th of June 1974, Iranian government spokesman and Minister of Information and Tourism Gholamreza Kianpour issued a strong official denial of the Shah’s comments in the French publication Les Informations regarding the possible Iranian acquisition of nuclear weapons. According to Kianpour, the Shah actually said Iran is not thinking of building atomic weapons but may revise its policy in this regard if other non-nuclear nations do. Kianpour also labeled false the Les Informations report that the monarch had implied India had neglected the welfare of its people in order to attain nuclear capability. The U.S. Embassy in Tehran commented that “Kianpour denial clearly indicates that current Iranian policy is not ... to acquire nuclear weapons. This is in keeping with previous [Iranian government] pronouncements and actions, including the signature and ratification of the Non-Proliferation Treaty and safeguards agreement. It may be that in interview with Les Informations the Shah wished to signal his concern about further proliferation and indicate that Iran could not stand idly by if other nations like Israel or Egypt should go nuclear.Shah's Alleged Statement on Nuclear Weapons, State Department Cable 1974 Tehran 5192, June 25, 1974.
US and European companies scrambled to do business in Iran. Bushehr, the first plant, would supply energy to the city of Shiraz. In 1975, the German firm Kraftwerk Union AG, a joint venture of Siemens AG and AEG, signed a contract worth $4 to to build the pressurized water reactor plant. Construction of the two 1,196 MWe reactora was to have been completed in 1981.
In 1975, Sweden's 10 percent share in Eurodif went to Iran. The French government subsidiary company Cogéma and the Iranian Government established the Sofidif (Société franco–iranienne pour l'enrichissement de l'uranium par diffusion gazeuse) enterprise with 60 and 40 percent shares, respectively. Sofidif acquired a 25 percent share in Eurodif, which gave Iran its 10 percent share of Eurodif. The Shah lent dollars, and another dollars in 1977, for the construction of the Eurodif factory, to have the right of buying 10 percent of the production of the site.
In 1976, US President Gerald Ford signed a directive offering Iran the chance to buy and operate a US-built reprocessing facility for extracting plutonium from reactor fuel. The Ford strategy paper said the "introduction of nuclear power will both provide for the growing needs of Iran's economy and free remaining oil reserves for export or conversion to petrochemicals."
A 1974 CIA proliferation assessment stated "If [the Shah] is alive in the mid-1980s ... and if other countries [particularly India] have proceeded with weapons development we have no doubt Iran will follow suit."
Post-revolution, 1979–1989 Following the 1979 Revolution, most of the international nuclear cooperation with Iran was cut off. Kraftwerk Union stopped work at the Bushehr project in January 1979, with one reactor 50 percent complete, and the other reactor 85 percent complete, and fully withdrew from the project in July 1979. The company said they based their action on Iran's non-payment of in overdue payments, while other sources claim it was due to American pressure.Internationalization of the Nuclear Fuel Cycle: Goals, Strategies, and Challenges (2009). Nuclear and Radiation Studies Board, National Academies Press.Russia: Nuclear Exports to Iran: Reactors Nuclear Threat Initiative The United States also cut off the supply of highly enriched fuel for the Tehran Nuclear Research Center, forcing it to shut down for a number of years. Eurodif also stopped supplying enriched uranium to Iran. Iran later argued that these experiences indicate foreign facilities and fuel supplies are an unreliable source of nuclear fuel supply.
In 1981, Iranian governmental officials concluded that the country's nuclear development should continue. Reports to the IAEA included that a site at Esfahan Nuclear Technology Center (ENTEC) would act "as the center for the transfer and development of nuclear technology, as well as contribute to the formation of local expertise and manpower needed to sustain a very ambitious program in the field of nuclear power reactor technology and fuel cycle technology." The IAEA also was informed about Entec's materials department, which was responsible for fabricating UO2 pellet fabrication, and chemical department, whose goal was the conversion of U3O8 to nuclear grade .Mark Hibbs, "US in 1983 stopped IAEA from helping Iran make UF6", Nuclear Fuel, 4 August 2003